The present invention relates to an optical system incorporated in a stereoscopic rigid endoscope.
Conventionally, a rigid endoscope has been widely used to observe inside of human bodies, machines, debris and the like. Conventional rigid endoscope has been provided with a single optical system and observation is performed with one eye. With such a conventional rigid endoscope, only a two-dimensional view can be observed. In order to carry out various treatment inside the object precisely, a three-dimensional view of the object is desired. For this purpose, recently, a stereoscopic rigid endoscope has been developed and used. An example of such a stereoscopic rigid endoscope is disclosed in Japanese Patent Provisional Publication No. 05-341207.
The stereoscopic rigid endoscope system described as a first embodiment in the publication is provided with a pair of object optical systems each including a polarization plate and a pair of eyepiece optical systems which respectively include polarization plates. According to the first embodiment, light passed through the objective optical systems are reflected by a pair of mirrors, which are arranged at opposite positions with a half mirror therebetween. The light reflected by the pair of mirrors is directed to the half mirror, by which the optical paths are combined to a single path. Then, the light is introduced to a tip end surface of a relay optical system. The light passed through and emerges from the proximal side end surface of the relay lens is divided to proceed along two different optical paths and is introduced into the pair of eyepiece optical systems, respectively. With use of the polarization plates, the polarized directions of the objective optical system and eyepiece optical system for right eye are aligned with each other, and the polarized directions of the objective optical system and eyepiece optical system for left eye are aligned with each other. Further, the polarization directions of the optical systems for right eye and left eye are adjusted to be perpendicular to each other.
According to a second embodiment in the publication, the stereoscopic rigid endoscope is provided with a single relaying optical system fixed in an insertion unit of the endoscope. In the vicinity of the distal end of the relaying optical system, an objective lens and a circular polarization plate are provided. In the vicinity of the proximal end of the relaying optical system, a polarization direction selecting device is provided. According to the second embodiment, the polarization plate is configured such that the polarization directions of a semi-circular area and the other of the semi-circular area are perpendicular to each other. The polarization direction selecting device is configured to alternately transmit two polarization components of the light emerging from the relaying optical system.
According to a third embodiment of the above-described publication, a pair of objective optical systems, which do not have the polarization plates, are provided at a tip portion of the insertion unit of the endoscope, and a polarization selecting device is provided in the vicinity of the proximal end of a relaying optical system which is fixed inside the insertion unit. According to the third embodiment, distances from the tip end surface of the insertion unit to each of the objective optical systems are the same, and the optical axes thereof are parallel with each other. Further, the optical axis of one of the objective optical systems coincides with the optical axis of the relaying optical system. The optical axis of the other objective optical system is finally arranged to coincide with the relaying optical system after bent by a mirror and polarization beam splitter in order. Further, the polarization beam splitter is configured such that the polarization direction thereof when the light is transmitted and the polarization direction when the light is reflected is perpendicular to each other.
As described above, in the stereoscopic rigid endoscope according to any one of the three embodiments, a single relaying optical system is used for both right and left eyes. Therefore, differences in optical performance for right and left eyes are suppressed.
However, according to the first embodiment, since the pair of mirrors are arranged on opposite sides of the half mirror. Therefore, it is difficult to downsize the tip end radius of the insertion unit.
According to the second embodiment, the right and left images are obtained by dividing a pupil of a single objective lens. Therefore, a substantially half of the diameter of the incident pupil of the objective optical system is regarded as a base length. The focal length of the objective optical system for the rigid endoscope is generally very short. Therefore, the incident pupil diameter is very small, and the stereoscopic rigid endoscope according to the second embodiment may not have a sufficient base length.
According to the third embodiment, an optical path lengths of the objective optical systems to the relaying optical system are different. Therefore, if the objective optical systems have the same optical performance, the incident pupils thereof do not locate on a same plane and object distances become different, which results in the difference of magnifications between the right and left optical systems. In other words, according to the third embodiment, the objective optical systems having the same optical performance cannot be used.